A method for producing a three-dimensional object is known as "stereolithography". In this method a layer of a liquid or a powderous material is applied to a support or a previously solidified layer and thereafter solidified by irradiating a focused light beam, for example a laser beam, at the points corresponding to the object. The object is produced in a layerwise fashion by successively solidifying a plurality of layers one after the other.
The EP-A-0 338 751 discloses such a method whereby supporting structures for supporting portions of the object or the entire object, respectively, are solidified together with the object itself.
When constructing supporting structures, however, the following problems are encoutered.
At filigree structures as well as intersections of planes several individual supports are generated because of the separate surface compounds in the CAD-model. The individual supports can be closely adjacent to each other and/or intersect or penetrate each other. For exposing the supporting structure the contour lines of the individual supports are scanned at an extremely small spacing which causes them to melt together. It is not possible or very difficult to remove the thus produced supporting structure without destroying the component.
In order to prevent the closely adjacent contour lines of individual supports from melting together, it is possible to scan the supports without contour. In this case, however, the exposure of the supports must be very hard i.e. a high degree of solidification must be produced to prevent the supports from fraying at the edges. Again, it is very labour-intensive to remove the thus produced supporting structure from the component, or it may even be impossible to remove it without destruction thereof. The DE 43 09 524 discloses a method for producing a three-dimensional object whereby the entire object or each layer of the object to be formed, respectively, is decomposed into an inner core region and an outer envelope region and the irradiation is controlled in the core region and in the envelope region so as to produce different characteristics in both regions. The decomposition of the object to be formed into an envelope region and a core region is made in a computer. Object data corresponding to the decomposition of the object to be formed into core and envelope region are provided to a further computer which controls an irradiation device for solidifying the layers of the object to be formed. The decomposition allows to construct an object using constructional forms which are different from each other and advantageous corresponding to the respective requirements.
The WO 94/07 681 discloses a method for producing a three-dimensional object by successive solidification of overlying layers of the object, whereby at first partial regions of a layer are solidified and joined with respective partial regions of the previously solidified layer therebelow to form multilayered cells and thereafter adjacent partial regions of one layer are joined by solidifying narrow web regions. It is thereby intended to reduce the deformation of the object.